Foldable tow bar

ABSTRACT

A car towing apparatus which, in its extended locked position, is a rigid tow bar attached to the front end of a towable vehicle and which subsequently can be folded into a compact structure and stored in a visually and non-obstructing, secured position to facilitate the vehicle being driven legally and safely on the highway.

The present Application is a Continuation of application Ser. No.08/253,626 filed Jun. 3, 1994 under the same title, now abandoned, whichin turn was a Continuation of application Ser. No. 08/015,262 filed Feb.8, 1993 under the same title, also abandoned, which in turn was aContinuation of application Ser. No. 07/885,904 filed May 18, 1992 underthe same title, also abandoned, which in turn was a Continuation ofapplication Ser. No. 07/768,478 filed Sep. 30, 1991 under the sametitle, also abandoned, which in turn was a Continuation of applicationSer. No. 07/568,276 filed Aug. 15, 1990 under the same title, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tow bars mounted on vehicles that maybe towed and more particularly to the type that can be folded into acompact package and stored on or adjacent to the front bumper.

2. Description of the Prior Art

The basic tow bar that has previously been available must be raised froma horizontal towing position to a vertical position when the towedvehicle is detached from a towing vehicle and driven or parked.Unfortunately, this partially obstructs the driver's vision,particularly i a compact type vehicle which is predominately towedbehind a motor home, van or the like. The alternative to this is thephysical removal of the tow bar from the towable vehicle and carried inthe car. This procedure is not only inconvenient from the standpoint ofsecurity for the detached tow bar, but also from the physical effortnecessary to accomplish such removal and replacement.

The number of individuals or families with a desire or need to tow avehicle behind a recreational vehicle is steadily increasing as agreater proportion of the population is spending more time travellingfor vacation and retirement activities. Convenience, safety and easy ofoperation of such apparatus becomes increasingly important in that anextremely high percentage of travelers on the highways today are seniorcitizens or retirees. Accordingly, in light of the above it is theobject of the present invention to provide a foldable tow bar that neednot be supported upright in line with the driver's vision but can bequickly folded and stored on the front end of a vehicle. The embodimentshown herein is of a new tow bar concept that can be modified from arigid towing position into a compact, stored and secure position on thetowable vehicle, with a minimum effort, when it is driven on the road.Since the tow bar remains attached to the towable vehicle at all times,there are no intermittant storage problems. Further, while in thesecured position on the vehicle, the tow bar cannot interfere with thedriver's vision. An outstanding feature of the telescopic arms androtating collars is that in an unblocked extended position the apparatusarms can be swung from side to side to line up with and hook onto thetowing ball. The towed vehicle can then back up against the stops in thearms at which time the lock pins can be replaced. This feature enablesthe towed car to hook-up with perfect alignment with the towing ball.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention in accordancewith the preferred embodiments thereof an improved tow bar apparatus isfolded and stored on a front end of a vehicular frame.

The tow bar apparatus comprises an elongated L-shaped beam, including anoutwardly extending lug mounted on the inside vertical surface and hasspaced ends secured on the front extended ends of a vehicular frame.There is a left end and right end mounting plate with openingstherethrough, and having a pair of adjoining contoured side edgesmounted vertically on the inside surface at the spaced ends of the beam.A finger-like upright extension mounted on the outside face of the rightend plate has a hole in the outer end. An elongated cylindrical tube issupported at the opposite ends in the plate openings. There is also aleft end and right end spaced collar rotatably mounted at opposite endson the tube. Upstanding ears are mounted on the left end and right endcollars to provide a hinge connection. On the bottom side of the rightend collar is a pawl-like projection, or arcuate-like lug for preventingsliding movement of the collar when engaged with a lug mounted on thebeam. Further, there is a left side and right side telescopic arm, andboth arms have a second square tube slidably enclosed in a first squaretube. The front end of the second square tube is connected to anelongated loop wherein stop means extending through the side walls ofthe first square tube limit travel of the second square tube. The rearends of the second square tubes are pivotally connected to the hingeconnection on the left end and right end collars. A coupler has aconventional towing ball hitch mounted thereon. One side of the coupleris pivotally connected to the outer end of the first square tube on theleft side and the other side is fixedly secured to the outer end of thefirst square tube on the right side. In operating the tow bar apparatusmeans is provided to fold the arms and coupler including unblocking andlocking means for storage on the extended frame. Similarly, there ismeans for unfolding the apparatus so as to extend the arms and couplerto a horizontal towing position.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of a preferred embodiment of the present inventionshown in towing position with the diverging arms locked in extendedalignment,

FIG. 2 is a vertical view of the arms depressed and unlocked forfolding,

FIG. 3 is a vertical view of the apparatus in the state of folding,

FIG. 4 is a folded view of the apparatus secured on a beam mounted onthe front end of a vehicular frame,

FIG. 5 is a vertical end view of FIG. 4,

FIG. 6 is a vertical view of a tube supporting plate on which afinger-like extension is attached,

FIG. 7 is a vertical view of a similar plate,

FIG. 8 is a vertical end view of a hinge collar showing spaced ears anda pawl-like lug attached thereon,

FIG. 9 is a vertical side view of FIG. 8,

FIG. 10 is a vertical end view of a coupling similar to FIG. 8,

FIG. 11 is a vertical side view of FIG. 10,

FIG. 12A is a horizontal side view of the pivotal connection of adiverging telescopic arm to the hinge portion of the collar and thepawl-like lug is engaged with the lug on the beam to hold the arm inrigid alignment,

FIG. 12B is a vertical view of FIG. A wherein the arm has been raised tounlock the lug on the collar with the lug on the beam,

FIG. 13 is a horizontal view of a sliding tube member of a telescopicarm having a slotted end portion,

FIG. 14 is a horizontal view of the tube disclosed in FIG. 13 slidablyenclosed in another tube of the arm, and

FIG. 15 is a horizontal view of the tubes in FIGS. 13 and 14 in extendedposition for towing.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

Referring to FIGS. 1 through 5 it can be seen that the towing bar 10 isa triangular structure comprising a ball coupler 11 pivotally connectedto a left side and right side diverging telescopic arms. The outer endsof the arms are likewise pivotally secured to an elongated baseassembly. The coupler 11 is adapted to fasten onto a ball connectionattached to a towing vehicle. The tow bar can be folded and stored onthe front of a vehicle's bumper.

The coupler 11 consists of a pair of spaced Y-shaped plates 12 and 13connected to a short length of square tubing, not shown, located in theneck portion 14. The tubing provides a solid section on which aconventional towing hitch can be mounted.

At the relatively flared rear end 16 of the coupler plate 13 andadjacent to the side edge 17 is a bolt hole 18 extending through bothcoupler plates. A bolt 19 inserted in the hole and threaded into a nut20, shown in FIG. 5, are used to connect the coupler 11 pivotally to thefront end 21 of a left side telescopic arm 22, the bolt 19 servingmeanwhile as a pivot in the connection at hole 18. Likewise, adjacent tothe opposite side edge 23 the front end 24 of a right side telescopicarm 25 is integrally secured to the coupler 11. Further, a short lengthof tubing 26 is mounted on plate 13 having an opening extending over theside edge 23. Also on plate 13, a handle 27 is mounted between hole 18and tube 26 having a hand hold parallel to rear end 16.

The left side arm 22 and right side arm 25 include a similar firstsquare tube 28 which has a stop pin hole 29 extending through the spacedsides of both square tubes 28 approximately intermediate of front andrear ends 21 and 30 respectively, on the first square tube 28 on theleft side and similarly between the front end 24 and rear end 30 on thefirst square tube on the right side of coupler 11. Another hole 31extending through parallel sides of both square tubes 28 for a lock pin31′, shown in FIG. 1, is located adjacent to rear end 30. A secondsquare tube 32 is slidably enclosed in first square tube 28 of arms 22and 28. Tube 32, shown in FIGS. 1, 2 and 3 comprises a length of squaretubing 33 and 33′, respectively to which is attached an elongated loop34 shown in FIGS. 13 and 15. Loop 34 has two spaced legs 35 forming aslot 36 between the connection of the legs to the front end 37 of tube33 and 33′ and the distal end 38 of loop 34. In the view of FIG. 13, itcan be seen that there is a hole 39 adjacent to the front end 37 andanother hole 40 adjacent to the rear end 41 of tubes 33 and 33′. Inassembling tube 33 and 33′ in tube 28 the tube is extended so that slot36 lays somewhere underneath the stop pin hole 29. A bolt similar tobolt 19 is inserted in hole 29 between the pair of legs 35 and fastenedwith a nut similar to nut 20 to provide stopping means so as to limitthe travel of the tube 33 and 33′ to the length of slot 36, shown inFIG. 14. Accordingly, as shown in FIG. 15, when arms 22 and 25 are fullyextended tube 33 and 33′ are partly withdrawn from tube 28. In thisposition the hole 39 in tubes 33 and 33′ are in alignment with thelock-pin hole 31 in tube 28. A pin 31′ inserted in holes 39 and 31 lockstubes 28, 33 and 33′ together in a rigid, extended position, referenceFIG. 1.

The rear end 41 of tube 33 is pivotally connected between a pair ofspaced ears 42 mounted on a left end rotatable collar 43. A bolt,similar to bolt 19, extends through holes 44 and 40, and threaded with anut similar to nut 20 to fasten tube 33 to collar 43. Similarly, tube33′ slidably enclosed in tube 28 of arm 25 has an end 41 pivotallyconnected between ears 46 mounted on right end rotatable collar 47. Theears 46 have a hole 45 extending therethrough in alignment with hole 40on square tube 33′. Left and right end collars 43 and 47 are first andsecond mounting elements, respectively, for mounting the tow bar on anelongated support member formed by an elongated tube 50, and arerotatably mounted adjacent to opposite ends 48 and 49 on an theelongated tube 50. Left end 48 is enclosed with a stop cap 51, andadjacent to the stop cap 51, elongated tube 50 is supported in opening52 of a left end mounting plate 53. Also, mounted adjafcent to collar 43on the inward side is a narrow stop ring 54 including a hole 55extending through the stop ring 54 and elongated tube 50. A typical boltinserted in hole 55 and fastened with a nut is used to contain collar 43in rotatable position between the ring 54 and cap 51. Likewide collar 47is rotatably and slidably mounted on the opposite end 49 of tube 50. Anarcuate lug or pawl 56 is secured on the bottom side of collar 47opposite of ears 46 and extends transversely thereto. Further, tube 50is supported in the opening 52 of a right end mounting plate 57 whichhas a square notch portion 58 removed from the top edge 59. Afinger-like extension 60 secured on the outside face 61 of the right endmounting plate has a portion extending above edge 59. The outer end ofthe extension 60 has a hole 64 through which a cotter pin 62, as seen inFIG. 4, can be inserted to fasten left side and right side arms 22 and25 to extension 60. Another hole 65 extends through tube 50 adjacent tooutside face 61, including a conventional nut and bolt that prevents thetube from slipping out of mounting plates 53 and 57.

The plates 53 and 57 have two adjoining edges rigidly secured to thespaced ends, not shown, of an L-shaped beam 66 shown in FIGS. 4 and 5.Left end plate 53, seen in FIG. 7, has side edges 67 and 68 contoured toengage the inside horizontal and vertical surfaces 69 and 70,respectively of L-shaped beam 66, shown in FIG. 5. The right end plate57, shown in FIG. 6, has two side edges 71 and 72 also contoured toconform to the inside surfaces of 69 and 70 of L-shaped beam 66.Connected to the inside vertical surface 70 of beam 66 is a stop lug 73,shown in FIGS. 12A and 12B. Lug 73 is adapted to engage the pawl 56 andsecure right end collar 47 in fixed position when tow bar 10 is inhorizontal towing position.

The folding of two bar 10 into a compact package for storing on thefront of a bumper is a fast and simple operation. To fold tow bar 10when unhitched from a towing vehicle the lock pin 31′ is withdrawn fromlock pin hole 31 located in square tube 33 and 33′. This allows squaretubes 33 and 33′ to slide freely in tube 28. It needs to be pointed outthat when tow bar 10 is in towing position the pawl 56 is locked behindstop lug 73 and right end collar 47 cannot slide on tube 50 therebyholding left and right side arms 22 and 25 in rigid extended alignment.Then holding the handle 27 on coupler 11 the lock pin 31′ is pulled fromhole 29 on square tube 28 and the tow bar can be swung from a horizontalto a vertical position while the square tubes 33 and 33′ are pushedinto, tube 28 until the front end 37 of square tubes 33 and 33′ abuttsagainst the stop pin 31, a bolt similar to bolt 19. FIG. 2 illustratesthe vertical condition whereby tubes 33 and 33′ and 28 are compressedtogether. The pawl 56 has rotated with right end collar 47 so as todisengage with lug 73 on beam 66 and move in front of the lug.Accordingly, collar 47 is now free to slide along tube 50. Referring toFIG. 3, it can be seen that left side and right side arms 22 and 25,respectively, are folding toward end 49 of tube 50 and that collar 47has moved a considerable distance toward left end collar 43. In FIG. 4,the tow bar is completely folded in a compact structure resting on frameextension 74. The collar 47 has moved along tube 50 to contact ring 54along side of tube 50. Further as shown in FIGS. 4 and 5, the small tube26 on coupler 11 has enclosed the upper portion of the finger-likeextension 60 whereupon a cotter pin 62 is inserted in hole 64 to locktow bar in folded position. The tow bar can be quickly unfolded andswung to the horizontal towing position by reversing the procedure citedfor folding the tow bar.

1. A tow bar adapted to be folded into a compact structure for storageadjacent to a vehicle front bumper prior to towing, which comprises: atow bar apparatus having spaced ends of an L-shaped beam secured toshort extensions on the front of a vehicular frame, the beam includinginside and outside vertical and horizontal surfaces with a lug extendingoutwardly from the inside vertical surface adjacent to a right end, Aleft end mounting plate and a right end mounting plate having outsideand inside faces and an opening therethrough, each left and right endplate including a pair of adjoining contoured side edges mountedvertically on the inside surfaces of said beam, and further including anupstanding finger-like extension with a lower end attached to theoutside face of the right end plate with a small hole including a cotterpin therein extending through the outer end of the extension, anelongated tube supported at the opposite ends in the left and right endmounting plate opening, a left end collar and a right end collar mountedrotatably on opposite ends of the elongated tube on the inside of saidleft and right end plates and including a pair of spaced flanges havinga hole therethrough for a hinge connection extending from the top, theright end collar also includes an arcuate lug on the bottom portionadapted to engage the lug on said L-shaped beam in a locked connection,a left side telescopic arm and a right side telescopic arm having a rearand front end, the rear end being pivotally connected to the hingeconnection on the left and right end collars, and the left and rightside arms consisting of a second square tube slidably enclosed in asimilar first square tube, and including means for locking eachtogether, a coupler comprising a pair of spaced Y-shaped platesseparated by a short length of square tubing and having a conventionaltowing hitch including a short length of round tubing mounted thereon,the coupler being connected to the front end of said left sidetelescopic arm and fixedly secured on the other side of the front end ofthe right side telescopic arm, whereby said left and right side arms inhorizontal towing condition being unlocked and raised vertically so asto initiate rotation of said left and right end collars on saidelongated tube which rotates said right end collar arcuate lug out ofthe locked connection with said L-shaped beam lug, and with downwardmovement the pivotal connection of said left and right side arms withsaid hinge connection of said left and right end collars urges saidright end collar to slide along said elongated tube from right to leftand bring said left and right side arms and said round tubing inenclosing contact with a finger-like extension on the outside face ofsaid right end plate, and whereby said coupler being released from saidfinger-like extension and raised upwardly to allow said right end collarto return to the right end of said elongated tube, and lowered so as torotate said left and right end collars and engage the locked connectionbetween said arcuate lug on said right end collar and said lug on saidL-shaped beam, whereby at horizontal level said left and right side armsmay be locked in rigid extension for towing.
 2. An apparatus as recitedin claim 1, wherein: said beam is an angle having an outside horizontalsurface secured to the short extensions.
 3. An apparatus as recited inclaim 1, wherein: said finger-like extension mounted on the outside faceof said right end plate is adapted to close with said short length ofround tubing disposed on the coupler and when fastened together with acotter pin serves to secure the left and right side arms in foldedposition.
 4. An apparatus as recited in claim 1 wherein: the secondsquare tube includes an elongated loop connected to one end of saidsecond square tube for limiting the travel of said second square tubewithin said first square tube.
 5. An apparatus as recited in claim 4,wherein: said first square tube includes a front and rear holetherethrough, and further included is a stop pin and a lock pin, thestop pin being located in said second square tube elongated loop and thelock pin being inserted in the rear hole is adapted to lock thereciprocal movement of said second square tube.
 6. An apparatus asrecited in claim 5, wherein: said coupler includes on one of theY-shaped plates a handle for lifting and folding the apparatus.
 7. Anapparatus as recited in claim 1, wherein: said right end plate includesa square notch in the top edge to receive and support the front end ofsaid right side arm therein when said left and right side arms andcoupler are locked and stored on said L-shaped beam.
 8. An apparatus asrecited in claim 1, wherein: said elongated tube includes a stop capthreaded on the left end adapted to enclosed the end of said tube and,further included is a narrow ring mounted on said tube for holding saidleft end collar in rotatable position.
 9. An apparatus as recited inclaim 1, wherein: said elongated tube also includes a hole extendingtherethrough adjacent to the outside face of said right end plate andinserted with a bolt threaded with a nut to prevent said right endcollar from sliding off said tube.
 10. A tow bar apparatus for use ininterconnecting a front end of a first vehicle to be towed with a secondvehicle for towing the first vehicle, comprising: means including acoupler and a pair of elongated first and second arms interconnectedwith the coupler to form a tow bar which has relatively extended andcollapsed positions when in and out of use, respectively, and means formounting the tow bar on a frame of the first vehicle adjacent the frontend thereof so that the tow bar can be extended and collapsed inrelation to the front end to assume the respective extended andcollapsed positions thereof when the tow bar is in and out of use,respectively, the coupler having means thereon with which to couple thetow bar to the second vehicle when the tow bar is in use, the pair ofelongated first and second arms each having relatively rearward andforward end portions which are telescopically engaged with one anotherso that each of the respective first and second arms is extensible andcontrollable relatively lengthwise thereof, the tow bar mounting meansincluding an elongated support member having spaced ends and alongitudinal axis extending from one of the spaced ends thereof to theother of the spaced ends thereof, means for mounting the elongatedsupport member on the front of the first vehicle so that the supportmember extends generally transverse the first vehicle adjacent the frontend thereof and the longitudinal axis of the support member is disposedin a horizontal line, a pair of mounting elements for mounting the towbar on the support member, a first of said pair of mounting elementsbeing engaged on the support member adjacent the one of the spaced endsthereof so as to be fixed against movement along the longitudinal axisof the support member, and a second of said pair of mounting elementsbeing slidably engaged on the support member between the first mountingelement and the other of the spaced ends of the support member so as tobe movable along the longitudinal axis of the support member betweenspaced first and second positions thereon relatively proximate to thefirst mounting element and relatively remote from the first mountingelement, respectively, the relatively rearward end portions of the firstand second arms being pivotally connected with the first and secondmounting elements, respectively, so that the respective first and secondarms are pivotable about the first and second mounting elements,respectively, in a plane of the support member substantially coincidingwith the longitudinal axis thereof, the relatively forward end portionof the first arm being pivotally connected with the coupler at a firstconnection therebetween having a pivot therein whose axis of rotation isrelatively transverse the plane of the support member, and therelatively forward end portion of the second arm being rigidly connectedwith the coupled at a second connection therebetween which is spacedapart from the pivot in the first connection so that when the tow bar isin the collapsed position thereof, and the respective first and secondarms are extended relatively lengthwise thereof, pivoted in relation toone another at the pivot in the first connection, and pivoted about thefirst and second mounting elements, respectively, in the plane of thesupport member, the second mounting element will move along thelongitudinal axis of the support member from the first position to thesecond position thereof on the support member to enable the coupler andthe respective arms to move relatively away from the support member sothat the tow bar can assume the extended position thereof relative ofthe front end of the first vehicle when the tow bar is in use, and whenthe respective first and second arms are thereafter contractedrelatively lengthwise thereof, pivoted in relation to one another at thepivot in the first connection, and pivoted about the first and secondmounting elements, respectively, in the plane of the support member, thesecond mounting element will move along the longitudinal axis of thesupport member from the second position to the first position thereof onthe support member to enable the coupler and the respective arms to moverelatively toward the support member so that the tow bar can resume thecollapsed position thereof relative to the front end of the firstvehicle when the tow bar is out of use, stop means for limiting themovement of the second mounting element along the axis of the supportmember to the respective first and second positions thereof on thesupport member, first releasable detention means for releasablydetaining the tow bar in the extended position thereof relative to thefront end of the vehicle when the tow bar is in use, and secondreleasable detention means for releasably detaining the tow bar in thecollapsed position thereof relative to the front end of the firstvehicle when the tow bar is out of use.
 11. The tow bar apparatusaccording to claim 10 wherein the support member is cylindrical and therespective first and second mounting elements are engaged thereon torotate about the longitudinal axis of the support member so that the towbar can be extended in relation to the front end of the first vehicle ina generally horizontal plane substantially coinciding with thelongitudinal axis of the support member when the tow bar is in use, andthen rotated into a generally vertical plane substantially coincidingwith the longitudinal axis of the support member when the tow bar is outof use.
 12. The tow bar apparatus according to claim 10 wherein the towbar mounting means also include a pair of generally spaced parallelfirst and second plates which are connected with the respective one andother of the spaced ends of the support member, respectively, transversethe longitudinal axis thereof, the first mounting element is engaged onthe support member adjacent the first plate, a collar is fixedly mountedon the support member between the first mounting element and the secondplate, the second mounting element is slidably engaged on the supportmember between the collar and the second plate, and the stop means areformed on the collar and the second plate to limit the movement of thesecond mounting element along the axis of the support member to firstand second positions thereon adjacent the collar and the second plate,respectively.
 13. The tow bar apparatus according to claim 12 furthercomprising an elongated beam rigidly interposed between the first andsecond plates in spaced parallel relationship to the support member, andwherein the support member is cylindrical and the respective first andsecond mounting elements are rotatably engaged thereon so that the towbar and the respective first and second mounting elements can be rotatedabout the longitudinal axis of the support member to an orientation inwhich the tow bar is extended in relation to the front end of the firstvehicle in a generally horizontal plane substantially coinciding withthe longitudinal axis of the support member when the tow bar is in use,and then the tow bar and the respective first and second mountingelements can be rotated from the generally horizontal plane into agenerally vertical plane substantially coinciding with the longitudinalaxis of the support member when the tow bar is out of use, and the firstreleasable detention means include lugs on the second mounting elementand the beam which are oppositely disposed to one another alongparallels to the longitudinal axis of the support member and engageablewith one another to prevent the second mounting element from movingtoward the first position thereof from the second position thereof onthe support member when the tow bar is rotated from the generallyvertical plane into the generally horizontal plane substantiallycoinciding with the longitudinal axis of the support member, anddisengageable from one another to release the second mounting elementfor movement toward the first position thereof from the second positionthereof on the support member when the tow bar is rotated from thegenerally horizontal plane into the generally vertical planesubstantially coinciding with the longitudinal axis of the supportmember.
 14. The tow bar apparatus according to claim 13 wherein thefirst releasable detention means also include pin and hole means forreleasably attaching the relatively rearward and forward end portions ofthe respective first and second arms to one another when the tow bar isin the extended position thereof.
 15. The tow bar apparatus according toclaim 14 further comprising means in the respective first and secondarms for positioning the respective pin and hole means in alignment withone another when the tow bar is in the extended position thereof. 16.The tow bar apparatus according to claim 13 wherein the secondreleasable detention means include means for releasably attaching thecoupler to the second plate when the tow bar is out of use in agenerally vertical plane substantially coinciding with the longitudinalaxis of the support member.
 17. The tow bar apparatus according to claim10 wherein the coupler has relatively forward and rearward ends in saidplane of the support member, and is Y-shaped between the relativelyforward and rearward ends thereof so as to have a neck portion adjacentthe relatively forward end thereof and a relatively flared portionadjacent the relatively rearward end thereof, and wherein the respectivefirst and second connections between the coupler and the relativelyforward end portions of the first and second arms are formed on therelatively flared portion of the coupler.
 18. The tow bar apparatusaccording to claim 10 wherein when the tow bar resumes the collapsedposition thereof, the first arm is adapted to be contractible relativelylengthwise thereof to a lesser length in one stage of contraction, andthe second arm is adapted to be contractible relatively lengthwisethereof to a length shorter than the lesser length of the first arm intwo successive stages of contraction.